To fabricate a photodetector that operates in a particular wavelength band, methods of crystallizing germanium on single-crystalline silicon deposited on an oxide insulating layer may be used.
However, crystallization carried out in this way may promote the formation of defects. For example, when germanium is crystallized on silicon having defects, the number of defects in germanium may also increase. Defects in the germanium may cause increases leakage current or dark current, which may adversely affect the characteristics of photo detectors.
It is known for photodetectors to include single crystalline germanium that is directly on a single-crystalline silicon layer on a silicon-on-insulator (SOI) substrate, so that the defects in germanium may be decreased.